Post-Earthquake Assessment and Strengthening of a Cultural-Heritage Residential Masonry Building after the 2020 Zagreb Earthquake

After a long period of no excessive ground shaking in Croatia and the region of ex-Yugoslavia, an earthquake that woke up the entire region was the one that shook Croatia on 22 March 2020. More than 25,000 buildings were severely damaged. A process of reconstruction and strengthening of existing damaged buildings is underway. This paper presents proposed strengthening measures to be conducted on a cultural-historical building located in the city of Zagreb, which is under protection and located in zone A. After a detailed visual inspection and on-site experimental investigations, modeling of the existing and strengthened structure was performed in 3Muri. It is an old unreinforced masonry building typical not only for this region but for relevant parts of Europe (north, central, and east). The aim was to strengthen the building to Level 3 while respecting the ICOMOS recommendations and Venice Charter. Some non-completely conservative concessions had to be made, to fully retrofit the building as requested. The structural strengthening consisted of a series of organic interventions relying on-in the weakest direction-a new steel frame, new steel-ring frames, and FRCM materials, besides fillings the cracks. Such intervention resulted in increasing the ultimate load in the X and Y directions, respectively, more than 650 and 175% with reference to the unstrengthened structure. Good consistency was obtained between the numerical modeling, visual inspection, and on-site testing.